1. Field of the Invention
The present invention relates to a parameter determination method, exposure method, device fabrication method, and storage medium.
2. Description of the Related Art
A projection exposure apparatus is used when fabricating a semiconductor device by using the photolithography technique. This projection exposure apparatus transfers a circuit pattern formed on a mask (or reticle) onto a photosensitive agent (resist) applied on a wafer by projecting the circuit pattern by using a projection optical system. The recent projection exposure apparatus uses the resolution enhanced technique in order to achieve micropatterning of semiconductor devices (i.e., to increase the resolution).
Examples of the resolution enhanced technique are the OAI (Off Axis Illumination) technique and OPC (Optical Proximity Correction) technique. The OAI technique forms an illumination shape (effective light source shape) into an annular shape or a multipole shape (for example, a dipole shape or quadrupole shape), and obliquely illuminates a reticle with the light. The OPC technique corrects the pattern shape of a reticle by using a lithography simulator in order to reduce the deterioration of the shape accuracy of a pattern to be formed on a wafer.
The lithography simulator is roughly classified into an optical simulator and process simulator (see Japanese Patent Laid-Open No. 2005-62750, Experimental Results on Optical Proximity Correction with Variable Threshold Resist Model (1997 SPIE Vol. 3051 pp. 458-468), and Mathematical and CAD Framework for Proximity Correction (1996 SPIE Vol. 2726 pp. 208-222)).
The optical simulator calculates a light intensity distribution (optical image) to be formed on the image plane of a projecting optical system while changing optical parameters (e.g., information pertaining to the reticle pattern and exposure conditions), thereby predicting a shape (resist image) to be formed on a resist. Accordingly, the optical simulator is generally used to determine the optical parameters.
On the other hand, the process simulator calculates a step of developing a resist exposed by an optical image while changing process (non-optical) parameters (information concerning the resist and processes), thereby predicting a shape (process image) to be formed after an etching process. In the process simulator, process models corresponding to actual processes, e.g., the photochemical reaction of a resist, an acid diffusion process performed by annealing (PEB), and patterning using a developer are prepared, and various parameters of these process models are fed back from the exposure results. Therefore, the process simulator is generally used to determine the process parameters.
Unfortunately, the conventional lithography simulators cannot simultaneously determine optical parameters and process parameters for implementing desired performance. Accordingly, the optical parameters and process parameters are independently determined such that the optical simulator determines the optical parameters, and the process simulator determines the process parameters. Recently, as micropatterning of semiconductor devices advances, it is getting harder to find the optical parameters and the process parameters to achieve desired image performance, and the mutual relationship between the optical parameters and process parameters becomes close. This makes it difficult to independently determine the optical parameters and process parameters, and prolongs the parameter determination time.